US 7744928 B2
Methods and compositions for inducing apoptosis of cells, such as macrophages, at a lesioned site of a body vessel are disclosed herein. Nitric oxide can be directly or indirectly delivered to a treatment site to increase macrophage apoptosis. Delivery can include site specific delivery of nitric oxide gas, nitric oxide in aqueous solution or a substance(s) which releases nitric oxide or causes nitric oxide to be generated from an endogenous source. Delivery can be achieved by a delivery system such as a catheter assembly, stent or other suitable device.
1. A method for treating a lesioned site in a body vessel comprising:
supplying a nitric oxide source comprising a nitric oxide in a gaseous state to a delivery cannula; and
delivering through the delivery cannula to a treatment site within a lumen of a body vessel the nitric oxide source.
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Methods and compositions for treating lesioned sites of atherosclerotic physiological vessels using nitric oxide sources.
“Arteriosclerosis” refers to the thickening and hardening of arteries. “Atherosclerosis” is a type of arteriosclerosis in which cells including smooth muscle cells and macrophages, fatty substances, cholesterol, cellular waste product, calcium and fibrin build up in the inner lining of a body vessel. If unstable or prone to rupture, the resultant build-up is commonly referred to as vulnerable plaque. It is generally believed that atherosclerosis begins with damage to the inner arterial wall resulting in a lesion. At the damaged site, substances such as lipids, platelets, cholesterol, cellular waste products and calcium deposit in the vascular tissue may accumulate, leading to plaque progression and potentially the formation of vulnerable plaque. In turn, these substances lead to recruitment of cells involved in the inflammatory cascade of the immune system, such as macrophages, which may release substances leading to plaque destabilization.
Artherosclerotic lesions are characterized by a high content of macrophages which contribute to atherosclerosis by, for example, releasing free radicals, synthesizing bioreactive lipids, synthesizing complement components, synthesizing coagulation cascade components, secreting proteases and protease inhibitors, secreting cytokines and chemokines and phagocytosis of apoptic cells.
“Apoptosis” is the disintegration of cells into membrane-bound particles that are then eliminated by phagocytosis or by shedding. Research studies suggest that nitric oxide induces macrophage cell apoptosis. For example, a recent study has shown that the oral administration of L-arginine, a substrate which releases nitric oxide, results in increased apoptosis of macrophage cells (Wang et al., 1999. Circulation 99; 1236-1241). Thus, macrophage apoptosis at lesioned sites of a body vessel is therefore desirable.
In accordance with embodiments of the present invention, nitric oxide can be directly or indirectly delivered to a treatment site or region of a body vessel to increase macrophage apoptosis. Delivery can include site specific delivery of nitric oxide gas, nitric oxide in aqueous solution or a substance(s) which releases nitric oxide or causes nitric oxide to be generated from an endogenous source, hereinafter collectively referred to as “nitric oxide sources.” Delivery can be achieved by a delivery system such as a catheter assembly, stent or other suitable device.
Methods and compositions for inducing apoptosis of macrophage cells at a lesioned site of a body vessel, such as a blood vessel, using nitric oxide sources are disclosed herein. It is to be understood that reference to a lesioned site of a blood vessel is intended to include the treatment of one or more lesioned sites, as well as treatment of one or more regions, treatment sites, or injury sites of a blood vessel. Thus, the use of such terms may be referred to interchangeably herein and are intended to be included within the scope of the present invention.
Methods for Inducing Macrophage Apoptosis
An excess amount of nitric oxide in macrophage cells can result in increased macrophage apoptosis. Under normal conditions, macrophage cells produce nitric oxide to regulate various biological functions. An overproduction of nitric oxide, however, may be toxic to macrophage cells resulting in apoptosis. In accordance with the present invention, nitric oxide can be directly or indirectly delivered to a treatment site 110 to increase macrophage apoptosis. Delivery can include site specific delivery of nitric oxide gas, nitric oxide in aqueous solution or a substance(s) which releases nitric oxide or causes nitric oxide to be generated from an endogenous source, or substances that increase the amount of nitric oxide produced endogenously. Delivery can be achieved by a delivery system such as a catheter assembly, stent or other suitable device.
In some embodiments, nitric oxide gas can be directly delivered to a lesioned site for treatment thereof. In some embodiments, nitric oxide gas can be diluted with a physiologically acceptable carrier gas for delivery to a lesioned site thereof. Representative examples of physiologically acceptable carrier gases include, but are not limited to, carbon dioxide, nitrogen, argon, helium, and perfluoro gases such as perfluoropentane or perfluoropropane. For example, small amounts of nitric oxide may be mixed into perfluoropropane before introduction into a vessel.
In some embodiments, nitric oxide gas can be mixed with a solvent (other than aqueous solutions such as saline or physiological buffers) which is physiologically suitable for injection for delivery to a lesioned site thereof. Such solvents include, but are not limited to, ethanol, dimethylsulfoxide, n-methylpyrrolidone, benzyl alcohol, benzylbenzoate and ethyl acetate. The solvent phase containing nitric oxide gas may be mixed with or emulsified into an aqueous solution such as saline. Alternatively, the nitric oxide may be mixed with one or more of a contrast agent, including, but not limited to, Omnipaque®, Imagopaque®, Optiray®, or Iopamidol®.
In some embodiments, nitric oxide gas can be mixed with aqueous solutions to create an aqueous solution for delivery to a lesioned site thereof. The solution may be partially saturated, saturated or super-saturated. A “saturated solution” is one in which a solvent has dissolved all of a solute possible at a given temperature. A “super-saturated solution” is one in which a solvent holds more solute than it normally holds at a given temperature as it is cooling down. A super-saturated solution may be stabilized by addition of surfactants such as PVA (poly vinyl alcohol), PVP (poly vinyl pyrrolidone), lipids, including phospholipids, amphiphilic polymers such as polyethylene glycol-polylactide (PEG-PLA) and ionic surfactants such as sodium dodecyl sulfate (SDS). Although nitric oxide has limited solubility in water (2-3 mM), it is believed that even a small or smaller quantity (e.g., less than about 2-3 mM) in solution delivered to a lesioned site can have beneficial effects.
In any of the above-described embodiments, the nitric oxide gas or nitric oxide gas solution may be encapsulated or formulated within a carrier for sustained release thereof. Carriers can include, but are not limited to, an implantable medical device, microspheres, nanoparticles, a gel or gel depot, a hydrogel or hydrogel depot, or a polymer or polymer depot for delivery and sustained release thereof. Carriers and methods of formulating substance-loaded carriers are known by those skilled in the art, an example of which can be found in U.S. Pat. No. 6,656,506 to Wu et al., incorporated by reference herein.
In some embodiments, L-arginine or polypeptides of L-arginine can be encapsulated or formulated within a carrier such as, for example, an implantable medical device, microspheres, nanoparticles, a gel or gel depot, a hydrogel or hydrogel depot, or a polymer or polymer depot for delivery and sustained release thereof. In the body of a mammal, nitric oxide is formed by the action of an endogenous enzyme, nitric oxide synthase (NOS), on L-arginine resulting in the production of nitric oxide and citrulline. Nitric oxide synthases includes endothelial nitric oxide synthase (eNOS, NOS I), inducible nitric oxide synthase (iNOS, NOS II) and neuronal nitric oxide synthase (NNOS, NOS III). iNOS is expressed in macrophages in response to various cytokines and microbial products. Once delivered to the treatment site, the L-arginine or polypeptides of L-arginine can diffuse from the carrier and provide more substrate by which iNOS can act upon to produce a greater population of NO within the localized treatment site. Other compounds suitable for formulation and delivery include, but are not intended to be limited to, L-arginine, L-homoarginine, and N-hydroxy-L-arginine, including their nitrosated and nitrosylated analogs (e.g., nitrosated L-arginine, nitrosylated L-arginine, nitrosated N-hydroxy-L-arginine, nitrosylated N-hydroxy-L-arginine, nitrosated L-homoarginine and nitrosylated L-homoarginine), precursors of L-arginine and/or physiologically acceptable salts thereof, including, for example, citrulline, ornithine, glutamine, lysine, polypeptides comprising at least one of these amino acids, inhibitors of the enzyme arginase (e.g., N-hydroxy-L-arginine and 2(S)-amino-6-boronohexanoic acid) and the substrates for nitric oxide synthase, cytokines, adenosine, bradykinin, calreticulin, bisacodyl, and phenolphthalein. For example, L-arginine may be encapsulated in nanoparticles of from between about 250 nm to about 300 nm in diameter by water-oil-water emulsification. In the emulsification process, L-arginine is dissolved in an aqueous solution, which is added to a polymer-solvent phase, for example polylactic glycolic acid (PLGA) dissolved in acetone. The aqueous phase containing the peptide is emulsified into the polymer phase by application of energy, for example by sonification. This emulsion is then added to an aqueous solution containing a small amount of an emulsifying agent such as poly-vinyl alcohol, and a water-oil-water emulsion is formed by addition of energy, for example by sonication. L-arginine loaded polymer particles are formed by removal of the acetone and may be lyophilized for storage.
In some embodiments, L-arginine and NOS can be encapsulated in an activated-release carrier such as a microsphere, nanoparticle, and the like. In some embodiments, the activated-release carrier can be permeable to both water and nitric oxide gas. Upon delivery, water can serve as the activating mechanism to start the enzymatic reaction of NOS on L-arginine. Once the reaction starts, nitric oxide gas can diffuse out of the activated-release carrier.
In some embodiments, a nitric oxide donor (NO donor), i.e., a nitric oxide-containing compound, and a suitable reactant (or no reactant) can be encapsulated in an activated-release carrier such as, for example, a microsphere, nanoparticle and the like. There are generally three kinds of mechanisms in which NO donors release NO: (I) spontaneously through thermal or photochemical self-decomposition; (II) chemical reactions with acid, alkali, metal and thiol; and (III) metabolic activation by NO synthases or oxidases. These NO donors may be mono-nitrosylated, poly-nitrosylated, mono-nitrosated and/or poly-nitrosated or a combination thereof at a variety of naturally susceptible or artificially provided binding sites for biologically active forms of NO.
In category I, for example, the NO donor can be the family of NONOates (diazeniumdiolates), which include, but are not limited to, O(2)-(2,4-Dinitrophenyl)1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K), N-FU/NONOate, S-nitrosocaptopril and Man-1-SNAP. In one example, JS-K can be attacked by the nucleophilic thiol group of glutathione resulting in the formation of a Meisenheimer complex. The NONOate moiety (4-carbethoxy-PIPERAZI/NO) then dissociates from the complex. At physiological conditions, the NONOate decomposes to release nitric oxide. Other examples include furoxanes.
In category II, for example, the NO donor can be a nitrite or nitrate such as sodium nitrite. A suitable reactant can include an appropriate reducing agent, such as sodium iodide, dithiothreitol, mercaptoethanol, iron particles, zinc particles, magnesium particles, sodium sulfide, sodium dithionite or sodium metabisulfite. When combined, the reducing agent reduces the nitric oxide donor such that the nitric oxide moiety disassociates from the metal ion. In some embodiments, the activated-release carrier can be permeable to both water and nitric oxide. Upon delivery, water can serve as an activator to start the reaction.
Other examples for NO donors are compounds comprising at least one ON—O—, ON—N— or ON—C— group. The compounds that include at least one ON—O—, ON—N— or ON—C— group are preferably ON—O—, ON—N— or ON—C-polypeptides; ON—O, ON—N— or ON—C-amino acids (including natural and synthetic amino acids and their stereoisomers and racemic mixtures); ON—O—, ON—N— or ON—C-sugars; ON—O—, ON—N— or ON—C— modified or unmodified oligonucleotides (comprising at least about 5 nucleotides, preferably from about 5 nucleotides to about 200 nucleotides); ON—O—, ON—N— or ON—C— straight or branched, saturated or unsaturated, aliphatic or aromatic, substituted or unsubstituted hydrocarbons; and ON—O—, ON—N— or ON—C-heterocyclic compounds. The term “polypeptide” as used herein includes proteins and polyamino acids that do not possess an ascertained biological function, and derivatives and mimics thereof.
Another group of NO donors include nitrates that donate, transfer or release nitric oxide, such as compounds comprising at least one O2 N—O—, O2 N—N—, O2 N—S— or O2 N—C— group. Preferred among these compounds are O2 N—O—, O2 N—N—, O2 N—S— or O2 N—C— polypeptides; O2 N—O—, O2 N—N—, O2 N—S— or O2 N—C—amino acids (including natural and synthetic amino acids and their stereoisomers and racemic mixtures); O2 N—O—, O2 N—N—, O2 N—S— or O2 N—C-sugars; O2 N—O—; O2 N—N—, O2 N—S— or O2 N—C— modified and unmodified oligonucleotides; O2 N—O—, O2 N—N—, O2 N—S— or O2 N—C— straight or branched, saturated or unsaturated, aliphatic or aromatic, substituted or unsubstituted hydrocarbons; and O2 N—O—, O2 N—N—, O2 N—S— or O2 N—C— heterocyclic compounds. Preferred examples of compounds comprising at least one O2 N—O—, O2 N—N—, O2 N—S— or O2 N—C—group include isosorbide dinitrate, isosorbide mononitrate, clonitrate, erythrityltetranitrate, mannitol hexanitrate, nitroglycerin, pentaerythritoltetranitrate, pentrinitrol and propatylnitrate.
In some embodiments, a nitric oxide generator (NO generator), i.e., nitric oxide-containing compound, and a suitable catalytic agent can be encapsulated in an activated-release carrier such as a microsphere or nanoparticle. Examples of NO generators include, but are not limited to, nitrosylated proteins with cysteine residues which allow for nitrosylation at the thiol group. Examples of catalytic agents include, but are not limited to, copper ion complexes which cleave NO moieties from nitrosylated proteins. Other examples for NO donor substrates are S-nitrosothiols, which are compounds that include at least one —S—NO group. These compounds include S-nitroso-polypeptides; S-nitrosylated amino acids (including natural and synthetic amino acids and their stereoisomers and racemic mixtures and derivatives thereof); S-nitrosylated sugars; S-nitrosylated, modified and unmodified, oligonucleotides; straight or branched, saturated or unsaturated, aliphatic or aromatic, substituted or unsubstituted S-nitrosylated hydrocarbons; and S-nitroso heterocyclic compounds. In some embodiments, the activated-release carrier can be permeable to both water and nitric oxide. Upon delivery, water can serve as an activator to start the reaction.
In some embodiments, a drug which inhibits the enzymes arginases I and II (arginase inhibitors) can be delivered to the lesioned site for treatment thereof. Arginases I and II control the production of nitric oxide from L-arginine by NOS I, II and III within macrophage cells. By inhibiting arginase I and II, more L-arginine will be available as a substrate to produce nitric oxide gas. Examples of arginase inhibitors include, but are not limited to, (S)-(2-Boronoethyl)-L-cysteine and Nω-Hydroxy-nor-L-arginine. In some embodiments, substrates such as antisense oligonucleotides or small interfering RNA (siRNA) can be introduced to macrophage cells at the lesioned site to reduce arginase expression.
The nitric oxide donors, generators, substrates or gas may be co-formulated with a variety of pharmaceutical excipients such as pharmaceutically acceptable organic or inorganic carrier substances suitable for parenteral application which do not deleteriously react with the active compounds. Examples of pharmaceutically acceptable carriers include, for example, water, salt solutions, alcohol, silicone, waxes, petroleum jelly, vegetable oils, polyethylene glycols, propylene glycol, liposomes, sugars, gelatin, lactose, amylose, magnesium stearate, talc, surfactants, silicic acid, viscous paraffin, perfume oil, fatty acid monoglycerides and diglycerides, petroethral fatty acid esters, hydroxymethyl-cellulose, polyvinylpyrrolidone, and the like.
In addition, nitric oxide donors, generators or substrates may be formulated for sustained release into an implantable medical device, micro- or nanoparticles made from polymer or ceramic materials, a gel or hydrogel depot or a polymer depot.
Delivery Systems and Methods
A variety of delivery systems known in the art can be used to deliver nitric oxide gas, nitric oxide solutions, or a substance(s) which releases nitric oxide or causes nitric oxide to be generated from an endogenous source, i.e., nitric oxide sources, to a treatment site. The delivery systems include, but are not intended to be limited to, regional, local and direct delivery systems and injection systems, in addition to stent deployment systems, and the like.
In one embodiment, catheter assembly 200 includes primary cannula 240 having a length that extends from proximal portion 220 (e.g., located external through a patient during a procedure) to connect with a proximal end or skirt of balloon 230. Primary cannula 240 has a lumen therethrough that includes inflation cannula 260 and delivery cannula 250. Each of inflation cannula 260 and delivery cannula 250 extends from proximal portion 220 of catheter assembly 200 to distal portion 210. Inflation cannula 260 has a distal end that terminates within balloon 230. Delivery cannula 250 extends through balloon 230.
Catheter assembly 200 also includes guidewire cannula 270 extending, in this embodiment, through balloon 230 through a distal end of catheter assembly 200. Guidewire cannula 270 has a lumen sized to accommodate guidewire 280. Catheter assembly 200 may be an over the wire (OTW) configuration where guidewire cannula 270 extends from a proximal end (external to a patient during a procedure) to a distal end of catheter assembly 200. Guidewire cannula 230 may also be used for delivery of a substance such as a nitric oxide source when guidewire 280 is removed with catheter assembly 200 in place. In such case, separate delivery cannula (delivery cannula 250) is unnecessary or a delivery cannula may be used to deliver one substance while guidewire cannula 270 is used to delivery another substance.
In another embodiment, catheter assembly 200 is a rapid exchange (RX) type catheter assembly and only a portion of catheter assembly 200 (a distal portion including balloon 230) is advanced over guidewire 280. In an RX type of catheter assembly, typically, the guidewire cannula/lumen extends from the distal end of the catheter to a proximal guidewire port spaced distally from the proximal end of the catheter assembly. The proximal guidewire port is typically spaced a substantial distance from the proximal end of the catheter assembly.
In one embodiment, catheter assembly 200 is introduced into blood vessel 100 and balloon 230 is inflated (e.g., with a suitable liquid through inflation cannula 260) to occlude the blood vessel. Following occlusion, a nitric oxide source is introduced through delivery cannula 250. By introducing the nitric oxide source, the nitric oxide source can absorb on the walls of the blood vessel at treatment site 110.
In an effort to improve the target area of nitric oxide sources to a treatment site, such as treatment site 110, the injury site may be isolated prior to delivery.
Catheter assembly 300 also includes guidewire cannula 370 extending, in this embodiment, through each of balloon 330 and balloon 335 through a distal end of catheter assembly. Guidewire cannula 370 has a lumen therethrough sized to accommodate a guidewire. No guidewire is shown within guidewire cannula 370. Catheter assembly 300 may be an over the wire (OTW) configuration or a rapid exchange (RX) type catheter assembly.
Catheter assembly 300 also includes delivery cannula 350. In this embodiment, delivery cannula 350 extends from a proximal portion 320 of catheter assembly 300 through a location between balloon 330 and balloon 335. Secondary cannula 365 extends between balloon 330 and balloon 335. A proximal portion or skirt of balloon 335 connects to a distal portion 310 of secondary cannula 365. A distal end or skirt of balloon 330 is connected to a proximal end of secondary cannula 365. Delivery cannula 350 terminates at opening 390 through secondary cannula 365. In this manner, a nitric oxide source may be introduced between balloon 330 and balloon 335 positioned adjacent to treatment site 110.
In the above embodiment, separate balloons having separate inflation lumens are described. It is appreciated, however, that a single inflation lumen may be used to inflate each of balloon 330 and balloon 335. Alternatively, in another embodiment, balloon 330 may be a guidewire balloon configuration such as a PERCUSURG™ catheter assembly where catheter assembly 300 including only balloon 330 is inserted over a guidewire including balloon 335.
Catheter assembly 400 also includes guidewire cannula 470 extending, in this embodiment, through balloon 430. Guidewire cannula 470 has a lumen therethrough sized to accommodate a guidewire. No guidewire is shown within guidewire cannula 470. Catheter assembly 400 may be an over-the-wire (OTW) configuration or rapid exchange (RX) type catheter assembly.
Catheter assembly 400 also includes delivery cannula 450. In this embodiment, delivery cannula 450 extends from a proximal end of catheter assembly 400 to proximal end or skirt of balloon 430. Balloon 430 is a double layer balloon. Balloon 430 includes inner layer 425 that is a non-porous material, such as Pebax®, Nylon or polyethylene terephthalate (PET). Balloon 430 also includes outer layer 435. Outer layer 435 is a porous material, such as extended polytetrafluoroethylene (ePTFE). In one embodiment, delivery cannula 450 is connected between inner layer 425 and outer layer 435 so that a nitric oxide source can be introduced between the layers and permeate through pores 490 in balloon 430 into a lumen of blood vessel 100.
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In any of the above-described embodiments, the nitric oxide source may be delivered to a treatment site through a delivery cannula. In some applications, the delivery cannula may be pre-loaded at the proximal end with a nitric oxide source, which may be a nitric oxide gas, a nitric oxide gas solution (aqueous or non-aqueous), an arginase inhibitor, or a carrier loaded with (a) L-arginine and optionally nitric oxide synthase, (b) a nitric oxide donor and suitable reactant or (c) a nitric oxide generator and suitable catalyst.
In some embodiments, the delivery system can be an implantable medical device deployment system such as a stent deployment system. Representative examples of implantable medical devices include, but are not limited to, self-expandable stents, balloon-expandable stents, micro-depot or micro-channel stents and grafts.
In some embodiments, a stent may be fabricated from a biocompatible metal or metal alloy. Representative examples include, but are not limited to, stainless steel (316L or 300), MP35N, MP2ON, Nitinol, Egiloy, tantalum, tantalum alloy, cobalt-chromium alloy, nickel-titanium alloy, platinum, iridium, platinum-iridium alloy, gold, magnesium or combinations thereof. MP35N and MP2ON are trade names for alloys of cobalt, nickel, chromium and molybdenum available from Standard Press Steel Co., Jenkintown, PA. MP35N consists of 35 percent (%), cobalt, 35% nickel, 20% chromium and 10% molybdenum. MP2ON consists of 50% cobalt, 20% nickel, 20% chromium and 10% molybdenum.
In some embodiments, the stent can be coated with a biocompatible coating which includes a nitric oxide source. The nitric oxide source may or may not be encapsulated in a sustained-release carrier or an activated-release carrier such as those described previously. Representative examples of polymers that may be used to manufacture or coat a stent, include but are not limited to, poly(N-acetylglucosamine) (Chitin), Chitosan, poly(hydroxyvalerate), poly(lactide-co-glycolide), poly(hydroxybutyrate), poly(hydroxybutyrate-co-valerate), polyorthoester, polyanhydride, poly(glycolic acid), poly(glycolide), poly(L-lactic acid), poly(L-lactide), poly(D,L-lactic), poly(caprolactone), poly(trimethylene carbonate), polyester amide, poly(glycolic acid-co-trimethylene carbonate), co-poly(ether-esters) (e.g. PEO/PLA), polyphosphazenes, biomolecules (such as fibrin, fibrinogen, cellulose, starch, collagen and hyaluronic acid), polyurethanes, silicones, polyesters, polyolefins, polyisobutylene and ethylene-alphaolefin copolymers, acrylic polymers and copolymers other than polyacrylates, vinyl halide polymers and copolymers (such as polyvinyl chloride), polyvinyl ethers (such as polyvinyl methyl ether), polyvinylidene halides (such as polyvinylidene chloride), polyacrylonitrile, polyvinyl ketones, polyvinyl aromatics (such as polystyrene), polyvinyl esters (such as polyvinyl acetate), acrylonitrile styrene copolymers, ABS resins, polyamides (such as Nylon 66 and polycaprolactam), polycarbonates, polyoxymethylenes, polyimides, polyethers, polyurethanes, rayon, rayon-tracetate, cellulose, cellulose acetate, cellulose butyrate, cellulose acetate butyrate, cellophane, cellulose nitrate, cellulose propionate, cellulose ethers, and carboxymethyl cellulose. Another type of polymer based on poly(lactic acid) that can be used includes graft copolymers, and block copolymers, such as AB block-copolymers (“diblock-copolymers”) or ABA block-copolymers (“triblock-copolymers”), or mixtures thereof.
Additional representative examples of polymers that may be especially well suited for use in manufacturing or coating stents include ethylene vinyl alcohol copolymer (e.g., EVOH or EVAL), poly(butyl methacrylate), poly(vinylidene fluoride-co-hexfluorapropene (e.g., SOLEF 21508, available from Solvay Solexis PVDF, Thorofare, N.J.), polyvinylidene fluoride (e.g., KYNAR, available from ATOFINA Chemicals, Philadelphia, Pa.), ethylene-vinyl acetate copolymers and polyethylene glycol.
In some applications, a polymer coating comprising at least one layer including a nitric oxide source can be applied to a surface of a stent for controlled release of the nitric oxide source. For example, a coating can include one or a combination of the following types of layers: (a) a treatment agent layer, which may include a polymer and a treatment agent, or alternatively, a polymer-free treatment agent; (b) an optional primer layer, which may improve adhesion of subsequent layers on the stent or on a previously formed layer; (c) an optional topcoat layer, which may serve to control the rate of release of the treatment agent; and (d) an optional biocompatible finishing layer, which may improve the biocompatibility of the coating. The treatment agent can be a nitric oxide source.
In some embodiments, the coating can be partially or completely applied to an abluminal surface or a luminal surface of the stent. The coating can be applied by methods known by those skilled in the art, including, but not limited to, dipping, spraying, pouring, brushing, spin-coating, roller coating, meniscus coating, powder coating, drop-on-demand coating, sputtering, gas-phase polymerization, solvent inversion or any combination thereof. Coating techniques are known by those skilled in the art.
In some embodiments, a stent may be fabricated from a bioerodable or biodegradable polymer to form a polymeric stent. Manufacturing processes for forming a polymeric stent include, but are not limited to, casting, molding or combinations thereof. Casting involves pouring a liquid polymeric composition into a mold. Molding processes include, but are not limited to, compression molding, extrusion molding, injection molding and foam molding. In compressing molding, solid polymeric materials are added to a mold and pressure and heat are applied until the polymeric material conforms to the mold. In extrusion molding, solid polymeric materials are added to a continuous melt that is forced through a die and cooled to a solid form. In injection molding, solid polymeric materials are added to a heated cylinder, softened and forced into a mold under pressure to create a solid form. In foam molding, blowing agents are used to expand and mold solid polymeric materials into a desired form, and the solid polymeric materials can be expanded to a volume in a range from about 2 to 50 times their original volume. In the above-described molding embodiments, the solid form may require additional processing to obtain the final product in a desired form.
In some embodiments, a nitric oxide source may be directly incorporated into the body of a polymeric stent during the manufacturing process. For example, a nitric oxide source may be combined with a polymer matrix and subsequently subjected to any of the above-described manufacturing process for formation thereof. In this aspect, the nitric oxide source may be released in a controlled manner as the polymeric stent naturally degrades over time.
From the foregoing detailed description, it will be evident that there are a number of changes, adaptations and modifications of the present invention which come within the province of those skilled in the part. The scope of the invention includes any combination of the elements from the different species and embodiments disclosed herein, as well as subassemblies, assemblies and methods thereof. However, it is intended that all such variations not departing from the spirit of the invention be considered as within the scope thereof.